While high functionalization of portable electronic equipment such as mobile phones, PDAs, DVCs and DSCs is being accelerated in recent years, reduction in size and weight has become indispensable in order for such products to be accepted in a market. Furthermore, in global warming, there are demanded products which are manufactured by use of least possible resources, and thereby pose no environmental burden. Naturally, lighter, thinner and smaller semiconductor devices are also required to achieve further reduction of materials.
Meanwhile, in order to meet the demand for thinner semiconductor devices, some semiconductor devices are manufactured without using thin metal wires, but by using conductive plates instead of flip chip mounting and the thin metal wires. Nevertheless, a technique for bonding the thin metal wires has been cultivated over a long history and is a highly reliable technique, thus being still employed.
For example, FIG. 8 is a cross-sectional view of a typical semiconductor device 100 constituted of a semiconductor chip 102 fixed onto an island 101, a lead 103 placed around the island 101 with one end of the lead 103 located close to the island 101, a thin metal wire 104A (or 104B) which electrically connects a bonding pad of the semiconductor chip 102 and the lead 103, a resin 105 which encapsulates the island 101, the semiconductor chip 102, the lead 103 and the thin metal wire 104A.
Two types of thin metal wires 104 are shown here. One shown by a dotted line is the thin metal wire 104A having a triangular loop, which has been employed since early times, whereas one shown by a solid line is the thin metal wire 104B having an M-loop.
The former thin metal wire 104A has a considerably high top portion 106. For this reason, in order to accommodate the semiconductor device 100 in a thin package, the top portion 106 needs to be lowered. However, when the top portion 106 is lowered, the thin metal wire 104A extended obliquely from the top portion 106 is likely to short-circuit to the semiconductor chip 102.
To avoid this, there has been invented a metal wire in such a shape that the height of a wire loop is reduced and additionally short-circuit to the semiconductor chip is prevented. This is called an M-loop, and disclosed in Japanese Patent No. 3276899, for example.
With reference to FIG. 7, a description is given of a method of manufacturing the thin metal wire 104B having a shape of the above mentioned M-loop. FIG. 7A is a view showing a trajectory of a capillary 150, and FIGS. 7B to 7H are views each showing what shape the thin metal wire forms in accordance with the trajectory. In addition, an arrow placed for the capillary 150 in FIG. 7B represents the reference numeral and the direction of the arrow in FIG. 7A. For example, the arrow 157 in FIG. 7B is the third arrow in FIG. 7A, and is marked with the same reference numeral. In other words, the arrow shown in FIG. 7B depicts a process of ascending of the capillary 150.
1. The capillary 150 undergoes first bonding, for example, onto a bonding pad 151 of a semiconductor chip, and subsequently moves as shown by arrows 155, 156 and 157. As shown in FIG. 7B, this causes a thin metal wire to form a thin metal wire extending obliquely to the right and then extending upward.
2. The capillary 150 is moved to the right as shown by an arrow 158 in FIG. 7A. This causes the thin metal wire to form a parabola protruding to the left, as shown in FIG. 7C.
3. The capillary 150 is moved upward up to a certain height as shown by an arrow 159 in FIG. 7A, is subsequently moved in a horizontal direction as shown by an arrow 160, and is further moved downward in a vertical direction as shown by an arrow 161. This forms a trough 165 in the center of the M-loop as shown in FIG. 7F.
4. The capillary 150 is moved in the vertical direction as shown by an arrow 162 in FIG. 7A, and the thin metal wire is held by a clamper provided together with the capillary 150 and undergoes second bonding onto an upper surface of the electrode 152 while forming a loop as shown by an arrow 163. This enables formation of the M-loop as shown in FIG. 7F.